It was an extremely simple refraction microscope
A microscope.
There is no instrument in world which measure how small an object is but instruments measure how large an object is .
laryngoscope
Microscope
A Telescope
microscope that see thing small.
telescope
A microscope
Telescope
telescope
Probably when you are really advanced in the first instrument. Also, when you can see similarities between the instruments and know how adapt what you have learned on the first instrument and apply it to the second.
A hydrometer is an instrument that measures the density of liquids. Auto batteries could be checked to see the strength of the acid in each cell before sealed batteries were made. I don't know of an instrument for solids or gases.